The present invention relates to an improved water heating apparatus employing a closed circuit heating system and an open circuit hot water supply system.
Hot water heating systems are known. A common system used in North America includes a large water storage tank that has means for heating the water prior to discharge to, for example a sink, shower, washing machine or the like. The water in such storage tanks is usually heated with electric heating coils or by burning hydrocarbon gas. Such storage tanks are advantageous because they can provide large amounts of hot water. In Europe, systems are used for rapidly heating cold water by passing it through a coiled copper tube that is positioned in a heating device. Such systems are relatively efficient but tend to be unable to provide large amounts of hot water. A combination of the two systems is shown in Canadian Patent Application 2125 070 to R. W. Smith which was published on Dec. 1, 1995. Basically, the Smith system uses a separate single-pass heater to supply hot water to a water tank. One of the limitations of the Smith system is the deposition of solids from potable water onto wetted heating surfaces. A method of providing a compact improved apparatus for supplying hot water to a tank and to alleviate the aforementioned deposition of solids is shown in U.S. Pat. No. 5,881,952 to Kenneth R. Macintyre and published on Mar. 16, 1995. The Macintyre system has a closed water circuit heater, and a liquid/liquid heat exchanger to transfer heat from the closed circuit water to pass-through water which is stored in a tank.
The present invention is intended to improve the efficiency of the aforementioned Macintyre system by combining the functions of a liquid/liquid heat exchanger and separate storage tank, in a single storage tank with internal coil, and by adding a heat exchanger to transfer sensible and latent heat from the heater flue gas to the pass-through water system.
Accordingly, the present invention provides a water heating apparatus with sensible and latent heat recovery comprising
(a) an air pass-through system comprising an air inlet, an air outlet, an air flow path extending from the air inlet to the air outlet, and a burner positioned in the air flow path for burning hydrocarbon fuel in the presence of oxygen in the air flow path;
(b) a water pass-through system comprising a water inlet for receiving water to be heated from a main water supply, a water outlet for discharging heated water, a water flow path extending from the water inlet to the water outlet, and a first heat exchanger positioned in the water flow path and in the air flow path downstream of the burner, for transferring sensible and latent heat from gases in the air flow path to water in the water flow path;
(c) a closed system for a liquid comprising a closed circuit, and second and third heat exchangers in fluid communication with each other within the closed circuit, the second heat exchanger being positioned within the air flow path proximate to the burner for transferring heat from gases in the air flow path to liquid in the closed circuit, and the third heat exchanger being positioned within the water flow path downstream of the first heat exchanger for transferring heat from liquid in the closed circuit to water in the water flow path;
(d) a recirculating water conduit having intake and output openings in fluid communication with said water flow path and, together with said water flow path, establishing a water recirculation circuit, through which water may be recirculated continuously past the first and third heat exchangers; and
(e) a control system comprising a mechanism operatively coupled to said systems and conduit for controlling air flow through said air pass-through system, water flow through said water pass-through system, liquid flow through said closed circuit, and water flow through said recirculating water conduit, a first fast response temperature sensor operatively connected to said water pass-through system for sensing the temperature of water flowing therethrough, a controller operatively coupled to said temperature sensor, burner, and mechanism and being adapted to interpret signals generated by the temperature sensor to determine whether there is a need to heat water in the water pass-through system and to respectively actuate the burner to heat air in the pass-through system and liquid in the closed system and recirculate water through the recirculating water conduit, when the need arises.
The advantage of this invention is that the efficiency of heating the pass-through water is increased by approximately 6% relative to the system taught in U.S. Pat. No. 5,881,952 to Macintyre.